全文获取类型
收费全文 | 917篇 |
免费 | 69篇 |
国内免费 | 46篇 |
专业分类
1032篇 |
出版年
2024年 | 4篇 |
2023年 | 12篇 |
2022年 | 23篇 |
2021年 | 46篇 |
2020年 | 26篇 |
2019年 | 37篇 |
2018年 | 31篇 |
2017年 | 28篇 |
2016年 | 43篇 |
2015年 | 66篇 |
2014年 | 59篇 |
2013年 | 66篇 |
2012年 | 62篇 |
2011年 | 67篇 |
2010年 | 22篇 |
2009年 | 31篇 |
2008年 | 43篇 |
2007年 | 31篇 |
2006年 | 38篇 |
2005年 | 26篇 |
2004年 | 17篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1968年 | 2篇 |
排序方式: 共有1032条查询结果,搜索用时 15 毫秒
91.
92.
April M. Weissmiller Orlangie Natera-Naranjo Sol M. Reyna Matthew L. Pearn Xiaobei Zhao Phuong Nguyen Soan Cheng Lawrence S. B. Goldstein Rudolph E. Tanzi Steven L. Wagner William C. Mobley Chengbiao Wu 《PloS one》2015,10(2)
Clues to Alzheimer disease (AD) pathogenesis come from a variety of different sources including studies of clinical and neuropathological features, biomarkers, genomics and animal and cellular models. An important role for amyloid precursor protein (APP) and its processing has emerged and considerable interest has been directed at the hypothesis that Aβ peptides induce changes central to pathogenesis. Accordingly, molecules that reduce the levels of Aβ peptides have been discovered such as γ-secretase inhibitors (GSIs) and modulators (GSMs). GSIs and GSMs reduce Aβ levels through very different mechanisms. However, GSIs, but not GSMs, markedly increase the levels of APP CTFs that are increasingly viewed as disrupting neuronal function. Here, we evaluated the effects of GSIs and GSMs on a number of neuronal phenotypes possibly relevant to their use in treatment of AD. We report that GSI disrupted retrograde axonal trafficking of brain-derived neurotrophic factor (BDNF), suppressed BDNF-induced downstream signaling pathways and induced changes in the distribution within neuronal processes of mitochondria and synaptic vesicles. In contrast, treatment with a novel class of GSMs had no significant effect on these measures. Since knockdown of APP by specific siRNA prevented GSI-induced changes in BDNF axonal trafficking and signaling, we concluded that GSI effects on APP processing were responsible, at least in part, for BDNF trafficking and signaling deficits. Our findings argue that with respect to anti-amyloid treatments, even an APP-specific GSI may have deleterious effects and GSMs may serve as a better alternative. 相似文献
93.
Developing new ABX3‐type perovskites is very important for expanding the family of perovskites and obtaining excellent light absorbing material. One strategy is replacing A site atoms with super‐alkali atoms for the perovskites, but super‐alkali perovskites with stable dynamics performance and high efficiency have not been found until now. Herein, massive super‐alkalis, such as Li3O, Li2F, H5O2, and so on, are introduced into the cubic CH3NH3PbI3 perovskites, and the perovskites with these super‐alkalis are systematically studied by using ab initio molecular dynamics simulation and density functional theory based first principles calculations. Calculated results indicate that the perovskites with the super‐alkalis including metal atoms show unstable dynamics performance under normal temperature and pressure. On the contrary, the first obtainable super‐alkali perovskites of cubic H5O2MBr3 (M = Ge, Sn, Pb) and H5O2PbI3 show stable dynamics performance. They also show suitable tolerance factors, negative formation energies, tunable direct band gaps, and small effective hole and electron masses. Moreover, the calculated power conversion efficiencies of 23.17% and 22.83% are obtained for the single‐junction solar cells based on the cubic H5O2SnBr3 and H5O2PbBr3 perovskites, respectively. 相似文献
94.
Identification of Differentially-expressed Genes in Intestinal Gastric Cancer by Microarray Analysis
95.
Long‐term administration of pyridostigmine attenuates pressure overload‐induced cardiac hypertrophy by inhibiting calcineurin signalling 下载免费PDF全文
Yi Lu Ming Zhao Jin‐Jun Liu Xi He Xiao‐Jiang Yu Long‐Zhu Liu Lei Sun Li‐Na Chen Wei‐Jin Zang 《Journal of cellular and molecular medicine》2017,21(9):2106-2116
Cardiac hypertrophy is associated with autonomic imbalance, characterized by enhanced sympathetic activity and withdrawal of parasympathetic control. Increased parasympathetic function improves ventricular performance. However, whether pyridostigmine, a reversible acetylcholinesterase inhibitor, can offset cardiac hypertrophy induced by pressure overload remains unclear. Hence, this study aimed to determine whether pyridostigmine can ameliorate pressure overload‐induced cardiac hypertrophy and identify the underlying mechanisms. Rats were subjected to either sham or constriction of abdominal aorta surgery and treated with or without pyridostigmine for 8 weeks. Vagal activity and cardiac function were determined using PowerLab. Cardiac hypertrophy was evaluated using various histological stains. Protein markers for cardiac hypertrophy were quantitated by Western blot and immunoprecipitation. Pressure overload resulted in a marked reduction in vagal discharge and a profound increase in cardiac hypertrophy index and cardiac dysfunction. Pyridostigmine increased the acetylcholine levels by inhibiting acetylcholinesterase in rats with pressure overload. Pyridostigmine significantly attenuated cardiac hypertrophy based on reduction in left ventricular weight/body weight, suppression of the levels of atrial natriuretic peptide, brain natriuretic peptide and β‐myosin heavy chain, and a reduction in cardiac fibrosis. These effects were accompanied by marked improvement of cardiac function. Additionally, pyridostigmine inhibited the CaN/NFAT3/GATA4 pathway and suppressed Orai1/STIM1 complex formation. In conclusion, pressure overload resulted in cardiac hypertrophy, cardiac dysfunction and a significant reduction in vagal discharge. Pyridostigmine attenuated cardiac hypertrophy and improved cardiac function, which was related to improved cholinergic transmission efficiency (decreased acetylcholinesterase and increased acetylcholine), inhibition of the CaN/NFAT3/GATA4 pathway and suppression of the interaction of Orai1/STIM1. 相似文献
96.
Lishan Wang Weidong Zang Jiang Liu Dongli Xie Weidong Ji Yaosheng Pan Zhiqiang Li Jiawei Shen Yongyong Shi 《PloS one》2013,8(4)
ObjectivesTo assess the association between the variant of Cytochrome P450 2A6 whole gene deletion (CYP2A6*4) polymorphism and risk of lung cancer.MethodsTwo investigators independently searched the PubMed, Elsevier, EMBASE, Web of Science, Wiley Online Library and Chinese National Knowledge Infrastructure (CNKI). Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) for CYP2A6*4 and lung cancer were calculated in a fixed-effects model (the Mantel-Haenszel method) and a random-effects model (the DerSimonian and Laird method) when appropriate.ResultsThis meta-analysis included seven eligible studies, which included 2524 lung cancer cases and 2258 controls (cancer–free). Overall, CYP2A6*4 was associated with the risk of lung cancer (allele*4 vs. allele non-*4, pooled OR = 0.826, 95% CI = 0.725−0.941, P-value = 0.004). When stratifying for population, significant association was observed in Asian (additive model, pooled OR = 0.794, 95% CI = 0.694−0.909, P-value = 0.001; dominant model, pooled OR = 0.827, 95% CI = 0.709−0.965, P-value = 0.016; recessive model (pooled OR = 0.444, 95% CI = 0.293−0.675, P-value <0.0001). In the overall analysis, a comparably significant decrease in the frequency of *4/*4 genotype was detected between cases and controls in Asian while no *4/*4 genotype was detected in Caucasian in collected data.ConclusionThis meta-analysis suggests that the CYP2A6*4 polymorphism is associated with susceptibility of lung cancer in Asian. The whole gene deletion of CYP2A6 may decrease the risk of lung cancer in Asian samples. 相似文献
97.
98.
99.
Sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) was used to characterize the H- and L-subunit ratios of several mammalian ferritins and one bacterioferritin. Traditionally, SDS-PAGE has been used to characterize the H- and L-subunit ratios in ferritin; however, this technique is relatively slow and requires staining, destaining, and scanning before the data can be processed. In addition, the H- and L-subunits of ferritin are fairly close in molecular weight (approximately 21,000 and approximately 20,000, respectively) and are often difficult to resolve in SDS-PAGE slab gels. In contrast, SDS-CGE requires no staining or destaining procedures and the peak quantitation is superior to SDS-PAGE. SDS-CGE is effective in quickly resolving the H- and L-subunits of ferritins from horse spleen, human liver, recombinant human H and L homopolymers, and mixtures of the two- and the single-subunit of a bacterioferritin from Escherichia coli. The technique has also proven useful in assaying the quality of the protein sample from both commercial and recombinant sources. Significant amounts of low-molecular-weight degradation products were detected in all commercial sources of horse spleen ferritin. Most commercial horse spleen ferritins lacked intact H-subunits under denaturing conditions. 相似文献
100.
Herwig Zang 《Journal of Ornithology》1980,121(4):371-386
Zusammenfassung 1969–1977 wurden in 15 Untersuchungsgebieten des Harzes, die sich auf die Höhenstufen von 100–900 m verteilen, brutbiologische Daten bei Trauerschnäpper, Sumpf-, Blau-, Kohl- und Tannenmeise gesammelt.Die Siedlungsdichte nimmt jeweils auf die Hälfte ab bei einer Höhenzunahme für die Sumpfmeise von 270 m, die Kohlmeise 195 m, die Tannenmeise 178 m und die Blaumeise 101 m (Halbwertshöhe).Die Verzögerung des Legebeginns bzw. des Schlüpftermins beträgt beim Trauerschnäpper 1,72, bei der Tannenmeise 1,68, der Sumpfmeise 1,97, der Kohlmeise 2,19 und der Blaumeise 5,24 Tage/100 m parallel zur vertikalen Verzögerung der Vegetationsentwicklung (Phänologie) von 1,8–2,6 Tage/100 m.Die Gelegegröße von Trauerschnäpper, Sumpf-, Blau- und Kohlmeise nimmt mit zunehmender Höhe linear um 0,14; 0,52; 0,51; und 0,11 Eier/100 m ab. Für die Kohlmeise ergeben sich Unterschiede in Laub- und Nadelwald, für die Tannenmeise zeigt sich eine Tendenz zur Zunahme mit der Höhe.Die Abnahme des Bruterfolges mit der Höhe beträgt beim Trauerschnäpper 0,22 flügge Junge/100 m, bei der Blaumeise 0,57, der Sumpfmeise 0,37, der Tannenmeise 0,23 und der Kohlmeise 0,13 flügge Junge/100 m. Für die Kohlmeise ergeben sich auch hier wieder Unterschiede in Laub- und Nadelwald.Für die Tannenmeise nimmt der Zweibrutanteil mit zunehmender Höhe linear um 3,6 %/100 m ab. Für die Kohlmeise zeigt er ebenfalls fallende Tendenz.Definiert man als vertikale Verbreitungsgrenze einer Art die Höhe, in der sich eine Population im Mittel noch stabil erhalten kann, so lassen sich aus der ermittelten Abnahme des Bruterfolges und den Werten für die Überlebensrate in einer vereinfachten Modellrechnung folgende Grenzen im Harz ermitteln: Blaumeise 500 m, Sumpfmeise 700 m, Kohlmeise 950 m, Trauerschnäpper und Tannenmeise 1000 m. Dies stimmt gut mit der Erfahrung überein.
The altitudinal influence on the population density and on the breeding biology ofFicedula hypoleuca, Parus palustris, P. caeruleus, P. major andP. ater in the Harz Mountains
Summary (a) Between 1967 and 1977, biological breeding data ofFicedula hypoleuca, Parus palustris, P. caeruleus, P. major andP. ater have been collected in 15 study areas of the Harz mountains, at altitude ranging from 100 m to 900 m.(b) The population density decreases by half, as a result of an increase in altitude of 270 m inP. palustris, 195 m inP. major, 178 m inP. ater and 101 m inP. caeruleus (halfvalue altitude).(c) The beginning of egglaying or hatching is delayed by 1.72 days per 100 m inFicedula hypoleuca; 1.68 days inP. ater; 1.97 days inP. palustris; 2.19 days inP. major and 5.24 days inP. caeruleus. These altitudinal retardations are parallel to that of the environmental vegetation (phenology) of 1.8–2.6 days per 100 m.(d) The clutch-size ofFicedula hypoleuca, P. palustris, P. caeruleus andP. major decreases by 0.14; 0.52; 0.51 and 0.11 eggs per 100 m increase of altitude respectively. InP. major, variations occur between deciduous and coniferous forests, and inP. ater the clutch-size tends to increase with an altitudinal increase.(e) The decrease in breeding success amounts to 0.22 fledglings per 100 m increase of altitude inFicedula hypoleuca, 0.57 fledglings inP. caeruleus, 0.37 fledglings inP. palustris, 0.23 fledglings inP. ater and 0.13 fledglings inP. major. Again, in the case ofP. major, differences occur between deciduous and coniferous forests.(f) The percentage of second broods ofP. ater decreases by 3.6 % per 100 m increase of altitude. The percentage of second broods ofP. major shows decreasing tendency, too.(g) When the altitudinal distribution limit of a species is defined as the level at which a population remains stable, the altitudinal decrease of breeding success and the mortality permit to draw up a simplified table of the altitudinal distribution limit. In the Harz these limits are as follows:P. caeruleus 500 m,P. palustris 700 m,P. major 950 m,F. hypoleuca 1000 m, andP. ater 1000 m. These results coincide with the experience.相似文献